Andromeda is the 19th-largest constellation in the sky. Its brightest star is Alpheratz (Alpha Andromedae), which shines at magnitude +2.1 and lies about 97 light-years away. For observers in the Northern Hemisphere, Andromeda is particularly well placed during the autumn months and reaches its highest point in the evening sky around November.
The constellation contains several notable deep-sky objects, ranging from nearby planetary nebulae to galaxies hundreds of millions of light-years away. Its most famous object is the Andromeda Galaxy, the nearest large galaxy to the Milky Way.
Andromeda Galaxy (M31, NGC 224)
Located about 2.5 million light-years away, the Andromeda Galaxy is the nearest large galaxy to the Milky Way. With an apparent magnitude of about 3.4, its bright central region can be seen without optical aid from a sufficiently dark location.
Andromeda is a huge spiral galaxy containing hundreds of billions of stars. Estimates of its total mass have changed as astronomers have improved their measurements, but M31 and the Milky Way are the two dominant galaxies of the Local Group.
M31 is accompanied by a substantial population of satellite galaxies. The best-known are M32 and M110, both of which appear close to Andromeda in the sky. Other satellites include NGC 147, NGC 185 and numerous much fainter dwarf galaxies. Modern surveys have identified dozens of small galaxies associated with the Andromeda system.
Messier 110 (NGC 205)
Messier 110 is a small elliptical galaxy located about 2.7 million light-years from Earth. It is one of the most prominent satellite galaxies of M31 and contains roughly 10 billion stars. Unlike many elliptical galaxies, M110 also contains clouds of gas and dust and evidence for a population of relatively young blue stars near its center.
The galaxy contains at least eight globular clusters. Despite extensive observations, there is no compelling evidence for the kind of massive central black hole found in many larger galaxies.
Charles Messier observed M110 in 1773 while studying the Andromeda Galaxy, although he did not include it in the published versions of his catalog. Caroline Herschel independently observed the galaxy in 1783. The designation M110 was eventually added to the modern Messier catalog in 1967 by astronomer Kenneth Glyn Jones.
NGC 891
NGC 891 is a large spiral galaxy seen almost exactly edge-on from Earth. Located roughly 30 million light-years away, it spans about 100,000 light-years and is often compared with the Milky Way because of its broadly similar size and spiral structure.
Its most striking feature is the dark lane of dust running through the galactic disk. Detailed observations also reveal filaments of dust extending far above and below the plane of the galaxy. These structures are associated with material being transported into the galaxy’s halo, with stellar winds and supernova activity among the processes thought to contribute.
Seen from our viewpoint, the edge-on orientation makes NGC 891 particularly useful for studying how gas and dust are distributed vertically through the disk and halo of a spiral galaxy.
Arp 65 (NGC 90 and NGC 93)
Arp 65 is a striking pair of interacting galaxies consisting of NGC 90 and NGC 93. The pair lies hundreds of millions of light-years away and forms part of a larger group of galaxies.
NGC 90 shows particularly obvious signs of gravitational disturbance. Its disk has been distorted and material has been drawn outward into extended structures, while regions of young blue stars reveal enhanced star formation. The system provides a good example of how close encounters can reshape galaxies without immediately causing them to merge.
Mayall II (G1)
Mayall II, commonly called G1, is an exceptionally massive globular star cluster orbiting the Andromeda Galaxy. It lies about 130,000 light-years from M31’s center and is the brightest globular cluster in the Local Group. Hubble observations have resolved many of its stars, revealing a population comparable in age to some of the oldest globular clusters in the Milky Way.
G1 is considerably more massive than a typical globular cluster and has long attracted interest because of its unusual properties. Studies have investigated whether it could contain an intermediate-mass black hole, although the evidence remains debated. Its complexity has also prompted suggestions that G1 may be the surviving nucleus of a dwarf galaxy that was stripped of its outer stars during interactions with Andromeda.
Blue Snowball Nebula (NGC 7662)
The Blue Snowball Nebula, also known as NGC 7662 or Caldwell 22, is a planetary nebula located about 2,500 light-years away. It formed when an aging star expelled its outer layers, leaving a hot stellar remnant at the center whose ultraviolet radiation causes the surrounding gas to glow.
NGC 7662 has an apparent magnitude of about 8.3. A small telescope can show it as a compact blue-green disk rather than a point-like star, while larger apertures and higher magnification reveal more of its structure. It can be found roughly one degree west of the 4th-magnitude star Kappa Andromedae.